Conventionally, electrical devices that are operated by means of an internal rechargeable battery are provided with means for enabling that battery to be recharged as necessary. In the past such devices have been provided with a charging socket and a charging adaptor. The charging adaptor is usually an AC/DC adaptor that is connected to the electrical mains supply and normally outputs to the charging socket a controlled DC supply voltage suitable for charging a particular battery.
A disadvantage with such conventional arrangements, however, is that with the proliferation in various types of portable electrical devices most users of such devices have to have a corresponding number of charging adaptors which may be mutually incompatible. Many charging adaptors may be designed to work with one device only.
To overcome this problem, at least one wireless charging platform has been proposed. One example of such a wireless platform is described in HUI, Ron, Shu-yuen, International Publication No. WO 03/105308 A1, entitled “Planar Inductive Battery Charger,” published on Dec. 18, 2003 (hereinafter referred to as “WO03/105308”), and which is herein incorporated by reference in its entirety. In this design, a planar wireless charging platform is proposed upon which devices to be charged may be placed. Underneath the surface of the charging platform there is an array of primary coils that generate lines of magnetic flux that extend generally perpendicular to the surface of the charging platform. A device to be charged (for example, a mobile phone) is provided with an integral (or external) secondary coil so that when the device is placed on the charging surface, magnetic flux passes through the secondary coil and generates a voltage therein. The voltage that is generated may be used to charge the battery within the device.
In principle, the arrangement disclosed in WO03/105308 is advantageous, since a large number of different devices can be charged (potentially simultaneously) by simply placing the devices on the single charging surface, and consequently the need for multiple charging adaptors can be reduced. In practice, however, there may still be some issues that need addressing for the charging platform of WO03/105308 to gain widespread acceptance. One issue, for example, is use of the charging platform with electrical devices that are not provided with an integral secondary coil. One approach to this is also described in WO03/105308 and uses adaptors that are provided with secondary coils that can receive magnetic flux from the surface of the charging platform and output a DC voltage to a conventional charging socket.
Furthermore, even with electrical devices provided with an integral secondary coil, for certain devices locating a secondary coil in a suitable position may be easier than it may be for other devices. It should be noted, for example, that for maximum efficiency, the secondary coil should be located in a plane such that when the device is placed on the charging surface, the secondary coil is parallel to the charging surface. This maximizes the magnetic flux passing through the secondary coil and increases the efficiency of the energy transfer. For electrical devices that have at least one generally planar surface, for example, a mobile phone, this may be quite easy to achieve as the secondary coil may be positioned parallel to the planar surface such that the electrical device can simply be placed on the charging surface with the planar surface in contact with the charging surface. In this way, the secondary coil will be close to and parallel to the charging surface.
However, for electrical devices of other shapes (especially devices with curved surfaces) finding a suitable location for the secondary coil may be less straightforward.